Hydrostatically driven machines typically include at least one hydraulic pump driven by an engine or motor. The hydraulic pump propels a flow of fluid to one or more actuators, typically hydraulic motors, connected to motivators, such as drums and/or wheels of the machine. The flow of fluid from the pump passes through each actuator, causing the drum and/or wheels to rotate at a given rate to move the machine along at a desired travel speed. An operator adjusting a control input, for example, a lever, pedal, or any other appropriate device controls the motion of the machine.
Hydrostatically driven compactors typically include at least one drum along a first axis and a second motivator, such as one or more wheels, disposed along a second axis. In compactors where a single hydraulic pump is provided, a complex system of sensors and electronics is generally utilized to control the relative rotary motions of the respective drum and wheels.
Alternate arrangements include two pumps that are coupled to the respective drum and wheels. While pump displacement is generally controlled by the operator, an orifice may be provided between the working sides of the pumps to balance the load during normal usage. The balance between these pumps can be adversely affected by changes in pressure resulting from, for example, machine operation on uneven terrain. When the compactor is moving uphill with the drum in the uphill position, the weight of the machine typically shifts somewhat off of the drum, forcing fluid across the orifice to the uphill pump, ultimately affecting the torque balance and speed between the respective motors. More particularly, the reduction in pressure on the uphill drum results in an increase in speed, causing the drum to spin. A similar result may occur when the drum is positioned downhill relative to the wheels. Other ground conditions that offer disparate traction or the like may likewise result in the spinning of either the drum or the wheels. For example, loose sand or the like may cause slippage that could result in such spinning. This spinning of one set of motivators, be it the drum or the wheels, causes an undesirable “uncompaction” of the soil below. In addition, the overdriving of one of the pumps may result in reduced part life in extreme conditions.
Similar conditions may result in other hydrostatically motivated machines that are propelled by a plurality of pumps coupled to respective axles, and coupled together by an orifice between working sides of the pumps to balance load during normal usage.
Accordingly, it is desirable to provide an arrangement that overcomes or minimizes one or more of these conditions or effects.